Depth control stop for air feed drills



Get 7, 1958 c. STRATMAN 2,854fiW1 DEPTH CONTROL STOP FOR AIR FEED DRILLSFiled Nov. 8, 1955 2 Sheets-Sheet 1 WILLIAM C STR ATMAN ATTORNEY 1958 w.c. STRATMAN DEPTH CONTROL STOP FOR AIR FEED DRILLS 2 Sheets-Sheet 2Filed Nov. 8, 1955 INVENTOR. WILLIAM C. STRATM AN wm/q ATTORNEY DEPTHCGNTRUL STOP FOR AIR FEED DRILLS William C. Stratrnan, Los Angeles,Calif., assignor to North American Aviation, Inc.

Application November 8, 1955, Serial No. 545,690

a Qiaims. (Ci. 77--34.5)

This invention relates to a control device for a machine tool and inparticular relates to an improved depth control stop for use on a rotaryairfeed drill.

Many of the airfeed drills in use at the present time in the aircraftindustry depend on a cumbersome, exposed, and extremely vulnerabledevice for controlling the amount of travel of the drill spindle and thedepth of the hole being drilled. Existing means for depth control forsuch drills generally consist of a poppet type bleed valve mountedtransversely relative to the drill longitudinal axis, by a clamp on alongitudinally extending cantilevered rod. An adjustable trip leverfixedly mounted on a reciprocating drill traverse rod moves with thetraverse rod, as the drill bit advances into the work, and contacts andopens the bleed valve whereby pressurized air is bled from the balancedtype drill control valve, the bleed valve and control valve beingintercommunicating, and the drill is shut oil. This arrangement is shownin Johnson Patent No. 2,607,197. By adjustably moving the bleed valvealong the cantilevered rod or by moving the adjustable trip lever on thetraverse rod the depth of the hole being drilled can be controlled.Maintenance of this depth control device has been found to constitute amajor problem throughout the industry and the number of air drillsnormally inoperative due to failures of the present type of depthcontrol device represents a considerable percentage of the total drillsin stock.

The cantilevered rod of the control device of the prior art is subjectto being bent out of alignment due to rough handling and its exposedlocation on the drill. This causes the bleed valve to be shifted out ofcentral alignment so that the trip fails to contact and operate thevalve and the drill continues to advance causing further bending andbreakage of the depth control elements, as well as often resulting in aruined work piece due to the hole being drilled too deep. Another sourceof difliculty with the present type of control device results fromsticking of the balanced type control valve on the airfeed drill. Suchsticking is caused by accidental blows and jars on the control valvehousing which deform the housing and cause the valve to hang up. Whenthis occurs the bleed valve is ineffective to halt the drill operationand the trip is brought to bear against the bleed valve member withincreasing force, as the drill continues to advance, causing bending andeventual breaking of the depth control elements.

In the present invention the cantilevered rod and bleed valve membermounted thereon are replaced by a heavy rigid valve body seated on theouter surface of the cylindrical drill extension barrel and secured tothe barrel by means of a nut mounted on a bolt or retainer having teethor serrations on the undersurface of the arcuate bolt head. The arcuatebolt head is mounted within the drill rear extension barrel, with thebolt shank extending radially outwardly through a slot in the barrel,and it engages serrations or teeth on the inner surface of a slottedsleeve mounted within the barrel. The

nited States Patent present invention thus provides a rugged, durablevalve block having provision for firmly attaching and positioning thevalve and valve block relative to the drill extension barrel. The valveblock is mounted symmetrically on the drill extension barrel about aplane passing through the drill axis, the valve axis and the valveactuator axis. In this manner the difiiculties and troubles encounteredwith the eccentric cantilevered mounting of the prior art are obviated.

Accordingly it is an object of this invention to provide an improvedairfeed drill depth control stop adaptable to existing equipment withoutfurther modification.

It is also an object of the invention to provide a positive actionairfeed drill stop that will require a minimum of maintenance.

It is a further object of the invention to provide an airfeed drill stopthat will not create a safety hazard through breakage of the stopdevice.

It is a still further object of the invention to provide a positiveaction airfeed drill stop of rugged construction that will stop theforward travel of the drill spindle even though the poppet type bleedvalve may have been rendered inoperative.

Still a further object of the invention is to provide an airfeed drillstop that will eliminate work spoilage due to overrunning of the drillin its forward travel.

These and other objects and advantages of the present invention willbecome apparent to those skilled in the art after reading the presentspecification and the accompanying drawings forming a part hereof, inwhich:

Fig. 1 is a longitudinal schematic showing, partly in elevation andpartly in section, of a rotary type airfeed drill incorporating thedepth control stop device of the present invention.

Fig. 2 is a transverse cross-sectional view taken in the plane of line22 in Fig. l and showing the valve block and its method of attachment torearward extension housing of the drill.

Fig. 3 is a longitudinal view, partly in elevation and partly in sectionand on an enlarged scale, taken substantially in the plane of line 3-3in Fig. 2, of the drill extension housing With the improved travelcontrol stop device mounted thereon.

Fig. 4 is a fragmentary top plan view, on a larger scale, of the drillextension housing and the valve block positioned thereon.

Fig. 5 is a transverse cross-sectional view taken in the plane of line55 in Fig. 3 and showing the valve trip device.

The device of this invention is for application to a pneumatic rotaryairfeed drill of the type disclosed in Taylor Patent 2,674,098 asmodified by an air control valve of the balanced type which may beunbalanced by means of one or more bleed type poppet valves, asdisclosed in Johnson Patent No. 2,607,197.

Referring specifically to the drawings, wherein like referencecharacters have been used throughout the several views to designate likeparts, and referring at first to Fig. l, the conventional type airfeeddrill comprises a cylinder 30 having pistons 31 and 32 spaced apart on arod 33 and disposed on opposite sides of a stationary abutment 34. Arotary air motor 35 guided for reciprocation in the forward end ofcylinder 3 is connected to piston rod 33 and drives tool spindle 35.Rearwardly of piston 32, the cylinder is provided with a transversepartition 38 forming the forward wall of an oil dashpot chamber 39having a piston 40 therein. The rear wall of chamber 39 is formed bypartition 41, both partitions 38 and 41 being centrally apertured forthe passage of piston rod 33. Reciprocable extension rod or member 17 isrigidly secured to the rear end of piston rod 33 and forms an axialcontinuation of the piston rod. Rod 17 is formed with two oppositelydiposed fiat sides for passage through a slot in an abutment at the rearend of cylinder 30 whereby rotation of rod 17 is prevented. Slottedsleeve 11 is concentrically positioned about rod 17 and both the sleeveand rod are covered by a tubular tail piece or cover having alongitudinal slot therein. Slotted sleeve 11 has a threaded internalsurface 13.

To control the supply and exhaust of air to and from the front and rearpiston chambers and also to the motor, a normally balanced two positionvalve 37 is used in conjunction with a spring loaded poppet type bleedvalve 3 for shifting valve 37 in a direction to unbalance the valve andcause operation of the drill to cease.

Travel control or stop device 24 of this invention comprises a valveblock or saddle member 1 having an arcuate lower surface with the samedegree of curvature as the outer surface of cylindrical cover 10, onwhich the saddle member seats. The rearward end of block 1 has alongitudinally extending valve bore 2 and threaded counterbore 25 toreceive the conventional type of air bleed valve 3 used in the existingdepth control stop on this type of drill. A bore is formed in theforward end of saddle 1 and is threaded to receive the connecting end offlexible conduit 19. Bores 2 and 20 communicate through angularly offsetconduits 21 and 26. Positioned between the longitudinally extendingbores 2 and 20 is a transverse bore 8 extending through saddle member 1from top to bottom.

Stop 24 further includes arcuate retaining member or bolt 4 having atoothed or threaded outer portion 5 and stud 6 attached to centerportion 7. Outer portion 5 is curved to fit within slotted sleeve 11 andthe threads on the outer surface thereof are adapted to engage internalthreads 13 on sleeve 11. Center portion 7 comprises a shorter piece ofarcuate shape and is dimensioned to fit slidably within slot 14 ofsleeve 11. Center portion 7 is brazed or otherwise rigidlyconcentrically attached to the outer surface of outer portion 5 with thethreaded outer ends of the latter projecting beyond the edges of centerportion 7. Stud 6 is rigidly attached to and projects radially outwardlyfrom center portion 7.

The remainder of stop device 24 comprises a trip 16 for attachment onextension rod 17. Trip 16 is of a sturdy, rugged construction andcomprises a lower enlarged end 29 having a threaded bore for engagingthreaded extension rod 17 and an arm portion 28. Arm 28 has a threadedbore near its upper end to receive threaded member 22 for operativelycontacting valve stem 18 of bleed valve 3. Member 22 can be moved in orout to provide for adjustment during initial installation and forsubsequent wear. Lock nut 23 secures member 22 in a fixed position whenthe latter is satisfactorily adjusted.

Stop device 24 is installed on the drill by removing cover 10surrounding slotted sleeve 11. Retainer member 4 is inserted withinsleeve 11 so that the toothed or threaded portion 5 engages the internalthreads 13 on sleeve 11 and center portion 7 fits within slot 14 withstud 6 projecting outwardly therefrom. Trip 16 is installed on extensionrod 17, with the head end of member 22 facing rearwardly, and ispositioned by means of the existing lock nuts 42 on the traverse rod.Cover 10 is then replaced on the drill with stud 6 of retainer 4 and arm28 of trip 16 projecting through slot 15 in cover 10. Saddle member 1 ispositioned over retainer 4 and on cover 10, with stud 6 projectingthrough bore 8. Nut 9 engages stud 6 to draw saddle member 1 downtightly on cover 10 while the toothed or threaded surface of retainerouter portion 5 is simultaneously brought into mating engagement with aportion of the threads 13 on slotted sleeve 11, whereby saddle member 1is rigidly secured in adjusted position on cover 10. By loosening nut 9the saddle and retainer assembly may be moved longitudinally along therear portion 12 of the drill to any desired location to suit the depthof hole to be drilled. A

4 flexible conduit 19 connects bore 20 with the drill air control valve37. Existing bleed valve 3 is threaded into bore 2 and member 22 isadjusted longitudinally for the depth of hole desired to be drilled orto compensate for wear resulting from prolonged usage.

In operation, trip 16, secured to extension rod 17 of the drill, isadvanced as the drill bit penetrates the work until the desired depth isreached. At this point trip 16 contacts stem 18 of bleed valve 3. Thisopens valve 3 to release the air pressure in conduit 19 and allows thespring loaded drill control valve 37 to which conduit 19 connects toreturn to the oif position, thus stopping the drill travel.

In the embodiment of the invention herein disclosed the bleed valvemounting consists of a relatively massive structure having a positivemeans for engaging the drill and is mounted with its longitudinal axisin the line of thrust of the trip device. This stop thus is notsusceptible of being sprung out of alignment as is the case with thepresent cantilevered type of bleed valve mounting. Furthermore in theevent that the drill control poppet type air valve becomes stuck orinoperative while in the run position and the operation of the bleedvalve will not shut off the drill, stop device 24 and trip 16 are of asufiiciently sturdy construction and have a sutficiently firm andpositive engagement with their coacting drill components that the drillbit will not be advanced after trip 16 abuts stop 24.

Thus it will be seen that this invention provides a sturdy, safe andpositive depth control stop that is not subject to misalignment ormalfunctioning as was the prior stop device.

While a particular embodiment of this invention has been illustrated anddescribed herein, it will be apparent that various changes andmodifications may be made in the construction and the arrangement of thevarious parts without departing from the spirit and scope of thisinvention in its broader aspects or as defined in the following claims.

I claim:

1. In a machine tool comprising a tool spindle, a fluid pressureoperated spindle reciprocating means, an axially extending elongatedcylindrical housing at the rear end of said tool, a first valve meanscontrolling the admission and exhaustion of air under pressure to andfrom said reciprocating means, a second valve means for bleedingoperating air pressure from the first valve means whereby thereciprocating means is rendered inoperative; and means attached to saidreciprocating means for operatively contacting and actuating said secondvalve means upon a predetermined amount of spindle travel; bolting meanssecured within said cylindrical housing and extending outwardlytherefrom, said second valve means having a valve body with acurvilinear surface complementary to the surface of said cylindricalhousing and being mounted and attached thereon by said bolting means.

2. In combination, a rotary air actuated drill comprising alongitudinally reciprocating axial member and a threaded sleeve rigidlymounted at one end of said drill enclosing said axial member, drilldepth control means comprising a valve adapted to bleed the operatingair pressure from said drill and thereby render the drill inoperative,said drill depth control means having a threaded portion threadedlyengaging said threaded sleeve and securing said depth control means tothe one end of said drill, and means rigidly attached to saidreciprocating member and positioned thereon to actuate said depthcontrol means and render said drill inoperative upon a predeterminedamount of movement of said reciprocating member.

3. In a rotary drill comprising a tool spindle, a fluid pressureoperated spindle reciprocating means, a rearward axial extension rod onsaid reciprocating means, a threaded axial sleeve surrounding therearward portion of said axial extension rod, a drill control valve ofthe balanced valve type controlling the admission and exhaust of airunder pressure to and from said reciprocating means; valve meanscommunicating with said drill control valve for bleeding operating airpressure from the same whereby said control valve may be moved to an offposition and the drill rendered inoperative, means attached to therearward portion of said extension rod for operatively contacting andactuating said bleed valve means upon a predetermined amount of drilltravel; said valve means including a valve block mounted directly on thesurface of said drill and a threaded portion engaging said threadedsleeve; and means on said threaded portion for joining said valve blockand said threaded portion into an assembly and securely attaching saidassembly at the surface of the rear end of said drill.

4. In a rotary drill comprising a tool spindle, a fluid pressureoperated spindle reciprocating means, a rearwardly extending axial rodon said reciprocating means, an internally threaded sleeve surroundingsaid rod, a slotted rearwardly extending housing surrounding said rodand said threaded sleeve, and a drill control valve of the balancedvalve type controlling the admission and exhaust of air under pressureto and from said reciprocating means; a spindle travel control meanscomprising a valve block adapted for mounting on the outer surfaces ofsaid housing and having a bleed valve positioned therein communicatingwith said drill control valve for bleeding operating air from the drillcontrol valve whereby the drill may be rendered inoperative, a boltingmember adapted to fit within the housing and engage said internallythreaded sleeve whereby the member is restrained against movement, saidvalve block being positioned on the surface of said housing and beingattached to said bolting member whereby said block is rigidly positionedon said drill, and means attached to said spindle reciprocating meansfor actuating said bleed valve upon predetermined movement of thereciprocating means to render said drill inoperative.

5. A rotary drill as described in claim 4 wherein said valve block has abore therethrough adapted to receive a stud and an arcuate lower surfaceadapted to seat on said rearwardly extending housing, and wherein saidbolting member has an arcuate transverse cross-section with a toothedupper surface thereon adapted to fit within and engage said internallythreaded sleeve, an integral stud projecting radially outwardly fromsaid member through the slotted housing and through said bore in thevalve block, and a nut locking said valve block and said bolting memberrigidly together on the drill.

6. In combination, a pneumatic rotary air feed drill comprising a drillcontrol valve, a rearwardly extending longitudinally reciproeable axialmember, and an elongated cylindrical housing extension of reduceddiameter at the rear end of said drill enclosing said member; drilldepth control means rigidly but adjustably clamped onto the curvilinearsurface of said cylindrical housing with the housing cylinder wall beingsecurely gripped between portions of said depth control means; and meansfor actuating said depth control means attached to said recipro eatingmember and positioned thereon to operatively contact said depth controlmeans upon a predetermined longitudinal movement of said reciprocatingmember whereby the fiow of pressurized air to said drill is interruptedand the drill thereby rendered inoperative, said depth control meanscomprising a bleed valve connected to said drill control valve adaptedto bleed the pressure therefrom.

References Cited in the file of this patent UNITED STATES PATENTS2,110,537 Tautz Mar. 8, 1938 2,607,197 Johnson n Aug. 19, 1952 FOREIGNPATENTS 198,473 Great Britain June 7, 1923 616,765 Great Britain Jan.26, 1949

